Applications running in other regions incur cross-region latency to read the latest data from the leader. If a little staleness for reads is acceptable for the applications running in the other regions, then Read Replicas is the pattern to adopt.
A read replica cluster is a set of follower nodes connected to a primary cluster. These are purely observer nodes, which means that they don't take part in the Raft consensus and elections. As a result, read replicas can have a different replication factor (RF) than the primary cluster, and you can have an even number of replicas.
Let's look into how this can be beneficial for your application.
SetupTo set up a local universe, refer to Set up a local YugabyteDB universe.
SetupTo set up a cluster, refer to Set up a YugabyteDB Managed cluster.
SetupTo set up a universe, refer to Set up a YugabyteDB Anywhere universe.
Suppose you have an RF 3 cluster set up in
us-east-2, with leader preference set to
us-east-1. And suppose you want to run other applications in
us-west. The read latencies would be similar to the following illustration.
Improve read latencies
To improve read latencies, set up separate Read Replica clusters in each of the regions where you want to run your application and where a little staleness is acceptable.
This enables the application to read data from the closest replica instead of going cross-region to the tablet leaders.
Notice that the read latency for the application in
us-west has drastically dropped to 2 ms from the initial 60 ms and the read latency of the application in
us-central has also dropped to 2 ms.
As replicas may not be up-to-date with all updates, by design, this might return slightly stale data (the default is 30 seconds, but this can be configured).
When the read replicas in a region fail, the application will redirect its read to the next closest read replica or leader.
Notice how the application in
us-west reads from the follower in
us-central when the read replicas in
us-west fail. In this case, the read latency is 40 ms, still much less than the original 60 ms.